It is known to separate biological fluids, such as aspirated bone marrow or peripheral blood, into their component parts, fractions, phases, or constituent layers by centrifugation. It is also known to provide mechanical devices comprised of a tube which houses a solid separator which, when actuated by centrifugal force, allows biological fluid to flow through or around the piston based on differing relative densities thereby separating the biological fluid into a one or more component parts above and one or more component parts below the solid separator. For example, when the biological fluid within the tube is blood, the centrifugation process results in a high density layer of red blood cells below the solid separator, a low density layer of plasma above the solid separator, and a buffy coat layer which defines an intermediate density layer or third fraction above the solid separator and below the low density layer of plasma.
One of the earliest solid separators was disclosed in U.S. Pat. No. 3,508,653, issued Apr. 28, 1970 to Coleman. That device was a rubber or other elastomeric cylinder. A major problem with that device was the inability to maintain a seal because it is costly to maintain the precise inner diameter of the test tube when mass produced. A subsequent solid separator development is disclosed in U.S. Pat. No. 3,814,248, issued Jun. 4, 1974 to Lawhead. Next, U.S. Pat. No. 3,779,383, issued Dec. 18, 1973 to Ayres disclosed a device in which the blood introduction end of the tube is opposite to the movable separator end of the tube, and abutting an impenetrable rubber closure. Following Ayres, U.S. Pat. No. 3,931,018, issued Jan. 6, 1976 to North, Jr. disclosed a solid separator for use in separation of blood serum and blood plasma using centrifugal force that must be inserted into the blood collection tube after blood collection.
In a patent to Levine, et al. (U.S. Pat. No. 4,159,896, issued Jul. 3, 1979) a centrifugally motivated solid separator device is disclosed in which a cylindrical float is disposed inside of a tube, which float has an accurately controlled outside diameter so as to fit snugly in the tube bore under static conditions. When used in harvesting blood cells the float is formed with an axial through bore which receives and expands the white cell and platelet layers in the blood sample after centrifugation thereof. The disclosed float was made from a plastic material having a specific gravity that causes it to float in the packed red cells after centrifugation of the blood sample in the tube.
In another patent to Levine, et al, (U.S. Pat. No. 5,393,674, issued Feb. 28, 1995) a clear plastic tube large enough to process 1 ml of blood and equipped with a cylindrical float and filled with an inert gas at low pressure is disclosed. The float contains a through bore, and prior to centrifugation, is held fixably at an initial location by tight contact between the exterior of the float and the interior wall of the tube. Unlike the inventions of Coleman, which contain pistons (or buoys) with no through bore, the Levine float relocates, under centrifugation, to a new position determined by its density relative to the density of the blood fractions as a result of the shrinkage of its diameter due to the longitudinal elongation (and subsequent lateral narrowing) of the float body that results from the substantial gravity gradient that occurs from the top to the bottom of the float. This substantial G force gradient (several thousand Gs) causes the float to elongate and narrow just as a rubber tube elongates and narrows when pulled from both ends. This space between the exterior of the float and the interior of the tube that develops during centrifugation provides the freedom of movement of the float consequent with the motion of the blood components to their new location determined by their density relative to the float. Levine does not posit, but it is assumed that some of the redistributing blood components also travel through the bore during centrifugation but since the top and bottom of the through bore are not closed, any cells and platelets that wind up there following centrifugation are easily infiltrated by the red cells and plasma during normal post centrifugation handling. Designed predominately as a diagnostic tool that proceeds through the visual examination of the cells that at least temporarily occupy the through bore right after centrifugation, Levine also discloses the possibility of extracting these cells with a syringe needle for additional diagnostic examination. This method of extraction necessarily is inefficient as a means of cell recovery as the intruding needle necessarily relocates the target cells above and below the through bore as it is inserted.
Hence, these known mechanical devices are generally capable of separating biological fluids into component parts or fractions; however, these devices are not very precise thereby resulting in inefficient separation of the biological fluid into component parts or fractions because of the substantial commingling of the separated fractions. Additionally, these known mechanical devices fail to provide a simple or efficient method to extract a fraction other than the top fraction of the sample leading to low recoveries, especially of the clinically important buffy coat fraction.
It is also known to provide more complicated mechanical devices in an attempt to alleviate the above known problems. For example, the patent to Leach, et al. (U.S. Pat. No. 7,374,678, issued May 20, 2008) in a first embodiment, discloses a device for separating a sample, such as blood, into a plurality of fractions. The device is comprised of a plunger (or second piston) which, prior to centrifugation, is retained proximate a top end of a closed ended distortable tube during centrifugation and a first piston (or buoy) which is tightly fitted near the bottom of the closed ended distortable tube such that under centrifugation with a sample of blood, the tube wall longitudinally compresses and bows outward thereby allowing the buoy to move in a direction of the top of the tube lifted by a layer of red blood cells of higher density than the piston that has flowed downward between the buoy and the interior of the tube wall. After centrifugation, the tube wall returns to its original dimension and traps this first piston at a new location coinciding with the interface position of a top plasma fraction and a bottom red blood fraction of the separated sample. On or near a collection face of this first piston (or buoy) is a third fraction which includes “a small, yet concentrated, amount of red blood cells, white blood cells, platelets, and a substantial portion of a buffy coat of the blood sample.” The device then employs a plunger (or second piston) which is manually pushed down into the tube from a location proximate the top end of the tube. The plunger (or second piston) includes a valve which allows the plasma to pass through the plunger to while the plunger is lowered to a predetermined depth above the first piston set by a depth gauge which locates the plunger a distance away from the collection face of the piston thereby defining a third fraction between a bottom face of the plunger (or second piston) and the collection face of the first piston. The extraction of the third fraction is accomplished via a vacuum created on a tube extending between a collection valve disposed in the top of the tube and a bore extending from the top of the plunger and the bottom of the plunger.
Accordingly, this device relies on the imprecise longitudinal compression and decompression of the tube wall in order to control the flow path between fractions and fails to contain the separated fractions until after centrifugation stops and the tube wall returns to its original dimensions. Furthermore, the extraction of the third fraction requires infiltration of the top plasma fraction. Hence, this recently patented device still fails to alleviate the problem of inefficient separation of the biological fluid into component parts or fractions and the commingling of the separated fractions.
In another embodiment, Leach, et al. discloses that the plunger (or second piston) is rigidly or slideably fitted with the first piston or buoy such that the pair is tightly fitted within the closed ended distortable tube wherein under centrifugation with a sample such of blood, the tube wall bows outward thereby allowing the pair to move in a direction of the top of the tube while lifted by a high density layer of red blood cells flowing downward between the pair and the interior of the tube wall. After centrifugation, the tube wall returns to its original dimension which grips the periphery of the first piston at an interface position of a plasma fraction and a red blood fraction of the separated sample. On or near a collection face of this first piston is “a small, yet concentrated, amount of red blood cells, white blood cells, platelets, and a substantial portion of a buffy coat of the blood sample.” The extraction of the intermediate (buffy coat) or third fraction is accomplished “by interconnecting a cannula or bored tube with the connection portion of the buoy cylinder” and connecting an extraction syringe to the cannula for creating a vacuum to draw the intermediate or third fraction from the space between the first and second pistons. This embodiment describes only one centrifugation spin, and fails to alleviate the problem of inefficient separation of the biological fluid into component parts or fractions and the commingling of the separated fractions. Furthermore, the extraction of a fraction other than the top fraction still requires the infiltration of at least one other fraction than the desired fraction to be extracted. Moreover, the device relies on the imprecise longitudinal compression and decompression of the tube wall in order to control the flow path between fractions and fails to contain the separated fractions until centrifugation stops and decompression of the tube wall is concluded.
Another problem associated with both embodiments of Leach, et al. is that the collection face, trough, or sump of the buoy must be shallow to be at a desired density level of the target buffy coat fraction and to preclude even further accumulation of reds cells with the target white cells and platelets to be extracted. Thus, this shallow trough results in having the target white blood cells and platelets, come to rest on the entire large surface area of the first piston on which the white blood cells and platelets tend to stick, which reduces the efficiency of the final collection step. A further problem associated with both embodiments of Leach, et al. is the time consuming and laborious process of fitting and interconnecting multiple parts to the device in order to perform the extraction process.
In general, current processes for separating and extracting fractions out of biological fluids require multiple steps that are both laborious and time consuming and that result in poor recoveries of the target white cells and platelets. Hence, it would be desirable to provide a simplified and more effective process so less time, labor, and training is required to do the procedure and fewer white cells and platelets are lost thereby providing a positive economic impact. A simplified process would also allow it to be performed in an intra-operative setting by an operating room nurse, rather than a remote laboratory setting by a technician so that a patient can be more rapidly treated and the possibility of mixing up samples can be essentially eliminated. Process simplification also has a direct correlation to process reproducibility that is also a problem with the known prior art.
Hence, the known prior art is problematic in a number of areas which include a deficiency in the recovery efficiency of cells of interest (target cells), in the selectivity of separation for reducing contamination or non-target cells from the target cell population, and in the multiple step, laborious, and time consuming extraction process.
Accordingly, there is a need to overcome the significant shortcomings of the known prior-art as delineated hereinabove.